1. Field of the Invention
The present invention relates to a solid-state image pickup device such as an optical sensor used in an image information processing apparatus such as a facsimile apparatus, an image scanner, a copying machine, an image sensor, or the like and, more particularly, to a solid-state image pickup device which converts not only visible light but also light in a invisible light range into an electrical signal.
2. Related Background Art
As a conventional solid-state image pickup device, a charge-coupled device (CCD) type device, a MOS type device, or an amplification type device in which a capacitive load is connected to the emitter of a phototransistor (U.S. Pat. No. 4,791,469 to Tadahiro Omi and Nobuyoshi Tanaka) is known.
Recently, solid-state image pickup devices have been used in various applications, and demand has arisen for a solid-state image pickup device having novel functions.
For example, recognition of a invisible image and reproduction and recording of the recognized image are required in addition to requirements for realizing a color copying machine with high image quality.
Such an image, i.e., a invisible light image includes, for example, an image formed by an ink having properties for absorbing infrared rays.
In general, a sensor for detecting invisible light is an independent device, and when it is used together with a sensor for detecting visible light, a new design concept is required.
The present inventors found, as a basic design concept, a technique for monolithically forming a visible light sensor and a invisible light sensor on a single semiconductor chip.
However, the above-mentioned techniques have room for further improvement.